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The present invention relates to low surface tension, low viscosity, aqueous, acidic compositions containing fluoride and organic, polar solvents for removal of photoresist and organic and inorganic etch or ash residues and processes for removal of photoresist and etch or ash residues. More particularly, the invention relates to a composition which is buffered having a pH value of between about 3 and about 6 and its use in removing photoresist and etch residue in processes operated at room temperature or above. The compositions of the present invention are free of glycols in general and in particular alkylene glycols and polyoxyalkylene glycols.
In the manufacture of semiconductors and semiconductor microcircuits, it is frequently necessary to coat substrate materials with a polymeric organic substance. Examples of some substrate materials includes, aluminum, titanium, copper, silicon dioxide coated silicon wafer, optionally having metallic elements of aluminum, titanium, or copper, and the like. Typically, the polymeric organic substance is a photoresist material. This is a material which will form an etch mask upon development after exposure to light. In subsequent processing steps, this polymeric organic substance (photoresist) must be removed from the surface of the substrate. One common method of removing photoresist from a substrate is by wet chemical means. The wet chemical compositions formulated to remove the photoresist from the substrate must do so without corroding, dissolving, or dulling the surface of any metallic circuitry; chemically altering the inorganic substrate; or attacking the substrate itself. Another method of removing photoresist is by a dry ash method where the photoresist is removed by plasma ashing using either oxygen or forming gas (hydrogen). In many instances the plasma ash method leaves residues or by-products. The residues or by-products may be the photoresist itself or a combination of the photoresist, underlying substrate and etch gasses. These residues or by-products are often referred to as sidewall polymers, veils or fences.
Various compositions for wet chemical removal of photoresists and organic and inorganic etch residues are known in the art. U.S. Pat. No. 5,698,503 discloses a composition for removing photoresist and residue, containing a polyhydric alcohol, ammonium fluoride, an organic polar solvent, water, and an acidic buffering compound, and acetic acid in an amount sufficient to obtain a pH of greater than about 4 and less than 7. The patent discloses propylene glycol and polyoxyalkylene glycols as the polyhydric alcohol and compositions such as, dimethylsulfoxide, dimethyl acetamide, N-methyl pyrrolidone and gamma butyrolactone as the polar solvents. U.S. Pat. No. 5,676,760 discloses processing semiconductor substrates with an electrolyte solution of ammonium chloride, ammonium acetate, ammonium fluoride, ammonium nitrate, ammonium bromide, ammoniun iodide, ammoniumsulphate, ammoniumoxalate, ammoniun carbonate, ammonium citrate, HCl, or ammonia and mixing it with deionized water. U.S. Pat. No. 5,571,447 discloses a composition for removing photoresist and residue containing a polyhydric alcohol, fluoboric acid, a fluoride containing compound and a polar solvent. The pH of the composition is less than 5. The patent discloses propylene glycol and polyoxyalkylene glycols as the polyhydric alcohol, and the polar solvent as preferrably water and/or dimethylsulfoxide. U.S. Pat. No. 5,320,790 discloses a method for selectively removing organometallic residues, native silicon oxides, or damaged silicon oxides created in processing by contacting a substrate with an essentially anhydrous composition of ammonium fluoride salt dissolved in a polyhydric alcohol. The patent discloses only glycols as examples of polyhydric alcohols. Compositions such as those described above exhibit a number of shortcomings. Solvent blends containing DMSO and fluoride (i.e., ammonium fluoride, HF, etc.) pose health risks to users due to the ability of DMSO to transport dissolved materials through the skin. Those solvent compositions containing glycols and a fluoride have a high surface tension ( greater than 40 mN/m) and a high viscosity ( greater than 40 cps) causing substrate wetting, spray or bulk distribution difficulties. In addition, many of the known compositions containing fluorides do not effectively remove photoresist at room temperature and at elevated temperatures exhibit unacceptably high oxide and metal etch rates. These compositions cannot be used at the contact or via level due to their high oxide etch rate and loss of critical control for patterns. It is the purpose of the present invention to provide compositions that exhibit little human or environmental toxicity; provide greater and more efficient ease of use; minimize corrosion of sensitive metals such as, aluminum, copper, titanium, and the like; and provide photoresist and residue removal at lower temperatures.
The compositions of the present invention are aqueous, buffered solutions with a pH of from about 3 to about 6, containing an organic polar solvent, a fluoride, an acidic buffer solution, and water. Glycols are not present in the compositions of the present invention and DMSO is not a preferred solvent because of the health risks attendant with its use in conjunction with the fluoride containing compositions of the present invention. The compositions of the present invention optionally include a corrosion inhibitor. The compositions of the present invention are used to remove photoresist and/or ash or etch residues formed during the processing of substrates used in the manufacture of semiconductor and microelectronic devices. The method of removal using the compositions of the present invention is carried out by contacting a substrate having photoresist and/or etch or ash residue on its surface with the compositions of the present invention. The actual conditions of the process depend among other things on the type of substrate and the material being removed. A general scheme for removal of a photoresist and/or etch or ash residue would consist of the steps of contacting a substrate with the composition of the present invention at temperatures of at least room temperature; maintaining contact between the substrate and the composition for a predetermined period of time; rinsing with water; and drying with an inert gas.
[NOT APPLICABLE]